A thin film transistor includes a gate electrode, a drain electrode, a source electrode, a dielectric film (an insulation layer) and an active layer (a semiconductor). In printed electronic devices, all of these components are manufactured by printing. At this time, the performance of a transistor depends on the charge mobility of the active layer and the on/off ratio, which is one of the main characteristics of the transistor, depends on the respective printed components of the transistor.
Up to now, the highest characteristics of the thin film transistor, 100% of which is manufactured using a printing process known around the world are that the mobility is 0.01 cm2/Vs and the on/off ratio is 106. At this time, an organic material is mainly used as the active layer and poly(3-hexyl thiopene) has shown the most stable value. Also, polyvinylphenol is used as the dielectric material, which is the insulation layer having an important influence on the on/off ratio.
To the contrary, the on/off ratio of the printed transistor using single walled carbon nanotubes (SWNTs) as network morphology is about 10. However, up to now, the mobility of this thin film transistor is relatively high (1˜200 cm2/Vs). Although printed SWNTs transistors have a high mobility, they cannot meet the requirements by the device to be used mainly due to their low on/off ratio. As a result, it is a very serious problem that should be overcome in order to commercialize the printed electronic devices.
Therefore, active studies have been made to a technology for applying various organic semiconductors. Among others, studies for applying single walled carbon nanotubes to the printed electronic devices have been in active progress since the charge mobility has been reported upto more than 10000 cm2/Vs when one single walled carbon nanotube has been used as a semiconductor. However, it is now difficult to apply the single walled carbon nanotubes to the printed electronic devices since metal component and semiconductor component are mixed in the single walled carbon nanotubes at a ratio of 1:3 when manufactured and a high-cost process is used to remove the metal component from the single walled carbon nanotubes and it is difficult to completely remove the metal component. Further, the transistor having the on/off ratio of 106 or more can be manufactured when using one single walled carbon nanotube on Si substrate, however, there is a fatal problem that the transistor cannot perform its role since a network is formed among the nanotubes and thus serves as a nano scale capacitor when massive single walled carbon nanotubes are used to print electronic devices.